Steerable radar antenna

ABSTRACT

A steerable radar antenna having a fixed energy feed requiring no rotary joints in the waveguide, including a microwave lens and a moveable reflector which operate conjunctively to collimate and direct the RF energy, and a drive means.

United States Patent 1 Migdal 1 Nov. 12, 1974 1 STEERABLE RADAR ANTENNAPrimar ExaminerJames W. Lawrence 1 t:Ph1N.MdlLM ,Clf. Y [75] men or uplg a a esa a 1 Assistant Examiner-T. N. Grlgsby [73] Assignee: Teledyne,Inc., San Diego, Calif. Attorney, A r Firm- Ralph S, Branscomb [22]Filed: Mar. 22, 1973 52] us. C1. 343/761, 343/911 L A steerable radarantenna having fixed energy feed 511' Int. Cl. HOlq 3/12, HOlq 15/08requiring rotary joints in the Waveguide, including [58] Field of Search343/761 757, 839 911 L a microwave lens and a moveable reflector which0perate conjunctively to collimatc and direct the RF en- [56] ReferencesCited ergy and a drive means.

I UNITED STATES PATENTS Q 3 Claims 4 Drawin Fi ures 1,931,980 10/1933Clavier 343/761 X I g g /-22 g 24 a 36 20 a 4..

STEERABLE RADAR ANTENNA SUMMARY OF THE INVENTION BACKGROUND OF THEINVENTION The present invention relates to scanning antennas, and moreparticularly to a steerable radar antenna which is suitable for mountingon an aircraft, or in any location where space is at a premium.

- In the prior art, scanning antennas generally utilize a rotatablereflector and primary radiator or feed system which rotates with thereflector during scanning. The primary radiator is coupled to a sourceof RF energy by means of a waveguide which requires one or two rotaryjoints therein to accomplish azimuth and/or elevation scanning of theantenna. Practical rotary joint design is difficult under the most idealconditions due to the inherent power loss in such a coupling, andbecomes even less practical in the design of a high power compact unitto be used in a high attitude aircraft capacity due to strictdimensional limitations.

One method devised to scan a radar beam without the use of rotary jointsis to couple a stationary RF feed to a stationary main reflector bymeans of a pivotal or rotatable subreflector. This method is useful whenan extremely high scan frequency is required, or in deep spaceapplications where the main reflector is so large that rotation is notpractical. However, the scanning arc of such an antenna is generallylimited to a relatively small solid angle due to the fixed nature of themain reflector, so the design is impractical for many uses, includingthat of present concern.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of atypical configuration of the antenna;

FIG. 2 is a sectional view taken online 22 of FIG.

FIG. 3 is a perspective view partially cut away, of an alternativeconfiguration; and

FIG. 4 is a sectional view taken on line 44 of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The feed provides a pointsource of circularly polarized RF energy and may consist of a flange 12which mates with a standard waveguide flange in the vehicle (not shown),a rectangular-to-circularwaveguide transition 14, and a polarizer 16.The feed will remain fixed with respect to the vehicles coordinatesystem, thereby eliminating the need for bulky rotary joints in thewaveguide.

In the first embodiment, shown in FIGS. 1 and 2, a microwave lens, morespecifically a Luneberg-type lens 18 comprising a hemisphere ofdielectric material, is disposed immediately above energy source 10 andis mounted on the reflector 20. The reflector is a flat circular platewith its underside flush against the plane of the great circle of thehemispherical lens 18. Reflector 20 could be other than planar toaccommodate a modified type of Luneberg lens, or to produce a differentmapping pattern.

Reflector 20 is pivotally mounted on a yoke 22 and an elevation driveassembly 24 is mounted on the upper surface of the reflector and engagesthe yoke for elevational steering of the reflector. The yoke 22 iscentrally mounted to an azimuth drive assembly 26 whose verticalscanning axis is collinear with the point source feed. The driveassemblies are conventional servo drive packages and are shown somewhatdiagrammatically in the drawings.

Azimuth drive assembly 26 is fixedly mounted on the underside of theradome cap 28 which is secured atop a cylindrical radome 30. Radome 30is mounted on frustoconical fairing 32 which is secured to the fin 34 orother portion of an aircraft, or any suitable frame member of a vehicle.

In the operation of the antenna illustrated in FIGS. 1 and 2semi-isotropic radiant energy emitted from the feed 10 is partiallycollimated by the lens 18, as indicated by the optical tracings 36, thenreflected by the reflector 20 back through lens 18 where it is furthercollimated, and is emitted from the antenna as an essentially parallelbeam. Upon reflection the sense of polarization is reversed so that thefinal emitted beam is circularly polarized in the opposite sense of thefeed. This reversal also occurs when the antenna is operating in itsreceiving mode.

Elevation steering is accomplished by elevation drive 24, which iscapable of positioning the reflector 20 approximately 30 above and belowthe 45 zero elevation command position as shown in phantom in FIG. 2,corresponding to a possible deviation of the emitted beam of plus orminus from the horizontal. Azimuth scanning capability of 360 isprovided by drive 26.

A modification of the antenna is shown in FIGS. 3 and 4, in which themicrowave lens takes the form of a circular Fresnel-type plate lens 38which is horizontally mounted at the junction between fairing 32 andradome 30. In this modification. as shown no elevation drive is providedso that reflector 40 is of elliptical form corresponding to the diagonalcross section of cylindrical radome 30. Azimuth scanning drive 26 isconnected directly to the upper surface of reflector 40, and again thescanning axis is collinear with the center of point source 10. Opticaltracings 42 in FIG. 4 indicate the path of the radiant energy as it isemitted from source 10, collimated by Fresnel lens 38, reflected andemitted as a parallel beam. Elevation scanning means could clearly beincluded without disrupting the parallelism of the emitted beam.

When used in its intended capacity, the unit will be mounted atop thetail section of an aircraft. Space stabilization signals computed fromvertical and heading gyro outputs combined with command elevation andazimuth signals in the steering unit will generate the drive signals forthe unit.

Both embodiments of the invention are simple, compact, and capable ofbeing mounted atop a narrow fin, the diameter of the microwave lensbeing on the order of 6 inches and the housing and drive structurescorrespondingly dimensioned. Other uses for the antenna, airborne,vehicular or terrestrial, are apparent, and the invention is notintended to be limited to the specific structure or mounting meansherein described.

LIST OF ASSIGNED NUMBERS OF PARTS 10. Feed 12. Flange Rectangular tocircular waveguide transitor l6. Polarizer 18. Luneberg lens ReflectorYoke Elevation drive assembly Azimuth drive assembly Radome cap Radomefairing Structural member of vehicle Optical tracings Fresnel-type lensReflector for 38 42. Optical tracing for 38 I claim:

1. A steerable radar antenna comprising:

a drive assembly;

a reflector having a generally hemispherical lens with the substantiallyplanar surface thereof mounted on the reflective surface of saidreflector, said reflector and lens comprising a unit operated by saiddrive assembly; and

at least one stationary feed disposed adjacent to the generallyhemispherical surface of said lens and capable of coupling RF energy tosaid lens 2. A steerable radar antenna comprising:

a drive assembly;

a reflector operated by said drive assembly;

a stationary punctiform feed for RF energy comprising:

an opemended waveguide;

21 rectangular-to-circular waveguide transition flanged to the open endof said waveguide;

a polarizer to produce circular polarization attached to said waveguidetransition such that circularly polarized energy is radiated from saidpo larizer generally in the direction of said reflector; and

a microwave lens disposed between said energy feed and said reflectordirecting said RF energy toward said reflector and cooperating with saidreflector to produce a collimated emitted beam.

3. A steerable radar antenna comprising:

a drive assembly;

a cylindrical radome;

an elliptical reflector diagonally disposed in said radome and operatedby said drive assembly;

a stationary feed to couple RF energy to said reflector; and

a Fresnel-zoned plate lens disposed between said energy feed and saidreflector.

1. A steerable radar antenna comprising: a drive assembly; a reflectorhaving a generally hemispherical lens with the substantially planarsurface thereof mounted on the reflective surface of said reflector,said reflector and lens comprising a unit operated by said driveassembly; and at least one stationary feed disposed adjacEnt to thegenerally hemispherical surface of said lens and capable of coupling RFenergy to said lens.
 2. A steerable radar antenna comprising: a driveassembly; a reflector operated by said drive assembly; a stationarypunctiform feed for RF energy comprising: an open-ended waveguide; arectangular-to-circular waveguide transition flanged to the open end ofsaid waveguide; a polarizer to produce circular polarization attached tosaid waveguide transition such that circularly polarized energy isradiated from said polarizer generally in the direction of saidreflector; and a microwave lens disposed between said energy feed andsaid reflector directing said RF energy toward said reflector andcooperating with said reflector to produce a collimated emitted beam. 3.A steerable radar antenna comprising: a drive assembly; a cylindricalradome; an elliptical reflector diagonally disposed in said radome andoperated by said drive assembly; a stationary feed to couple RF energyto said reflector; and a Fresnel-zoned plate lens disposed between saidenergy feed and said reflector.